Objective: Leptin receptors are abundant in human skeletal muscle, but the role of leptin in muscle growth, development and aging is not well understood. Here we utilized a novel mouse model lacking all functional leptin receptor isoforms (POUND mouse, Lepr(db/lb)) to determine the role of leptin in skeletal muscle.
Methods and findings: Skeletal muscle mass and fiber diameters were examined in POUND mice, and primary myoblast cultures were used to determine the effects of altered leptin signaling on myoblast proliferation and differentiation. ELISA assays, integrated pathway analysis of mRNA microarrays, and reverse phase protein analysis were performed to identify signaling pathways impacted by leptin receptor deficiency. Results show that skeletal muscle mass and fiber diameter are reduced 30-40% in POUND mice relative to wild-type controls. Primary myoblast cultures demonstrate decreased proliferation and decreased expression of both MyoD and myogenin in POUND mice compared to normal mice. Leptin treatment increased proliferation in primary myoblasts from muscles of both adult (12 months) and aged (24 months) wild-type mice, and leptin increased expression of MyoD and myogenin in aged primary myoblasts. ELISA assays and protein arrays revealed altered expression of molecules associated with the IGF-1/Akt and MAPK/MEK signaling pathways in muscle from the hindlimbs of mice lacking functional leptin receptors.
Conclusion: These data support the hypothesis that the adipokine leptin is a key factor important for the regulation of skeletal muscle mass, and that leptin can act directly on its receptors in peripheral tissues to regulate cell proliferation and differentiation.